1. Field of the Invention
This invention relates to computer hardware, and more particularly, the use of certain signals to detect the presence of add-in circuit cards.
2. Description of the Relevant Art
In many computer systems, additional functionality is often provided by add-in circuit cards. Such cards are typically coupled to a host computer system through one of several connectors on a computer motherboard. One of the most common types of add-in cards is the memory module. Memory modules typically include a plurality of memory chips mounted upon a small, compact circuit board, which may be inserted into a connector on a computer motherboard or other type of host board. Memory modules are typically used to expand the main memory capacity of a computer system. Memory modules may also, in some cases, be used to expand the cache memory of a computer system.
When a memory module is inserted into a computer system, its presence must be detected before the additional memory capacity may be utilized. The memory module must also receive power in order to perform its intended function. Many memory modules are configured to drive signals to the host computer system indicating that they are present (i.e. a presence detect signal) and receiving the required power (i.e. a power detect signal). Power detect signals are often times driven by a power detector circuit which is configured to detect the presence of an operating voltage for the memory module.
A common configuration for providing a presence detect signal involves connecting a ground pin on a memory module to a signal line of a host board, such as a computer motherboard. The signal line is initially held in a logic-high state by a pull-up resistor. When the module is connected to the host board, thereby connecting the ground pin to the pulled-up signal line, the signal line transitions to a logic-low state.
Current trends in the computer industry are towards larger bus structures (i.e. larger data and/or address buses). In some cases, this trend may lead to a demand for increased signal density for newer memory modules. In many cases, memory modules must be designed to fit into existing connectors, and thus the physical dimensions of the module must be held constant with respect to previously designed memory modules. Designers of memory modules must often times contend with these conflicting demands.
The problems outlined above may in large part be solved by a system and method for providing a common power detect and presence detect signal, in accordance with the present invention. In one embodiment, a memory module includes a voltage regulator and a power detector circuit. The voltage regulator may be configured to provide a stable operating voltage to the various circuits of the memory module. The power detector circuit may be configured to detect the presence of the operating voltage from the output of the voltage regulator. The power detector circuit may assert an output signal in response to a detection of a voltage from the voltage regulator. The output signal asserted by the power detector circuit may then be driven through a single pin of a connector mounted to the memory module to a storage unit of the host computer system. The storage unit may be configured to store the state of the output signal. Instructions executed by a central processing unit (CPU) of the computer system may cause the state of the output signal to be periodically read from the storage unit, providing an indication as to whether the voltage regulator is providing the operating voltage. If the memory module is not receiving the correct operating voltage, or it is not present, an indication of this condition may be provided to a user of the computer system. This indication may notify the user that service is required in order to ensure that a properly functioning memory module is present.
If the state of the signal stored in the storage unit indicates that a memory module is present and receiving the correct operating voltage, a host computer system may then begin utilizing the additional memory capacity provided by the memory module.
Thus, in various embodiments, the system and method of providing a common power detect and presence detect signal may provide an indication to a computer user as to whether or not a memory module is present and receiving an operating voltage. By using a single signal pin and signal line to convey the output signal, circuit board area may be saved.